There is an ongoing work item by the Third Generation Partnership Project (3GPP) for the introduction of a low complexity, low cost user equipment (UE) type for machine type communications (MTC) in Long Term Evolution (LTE) Release 12 (Rel-12). One of the complexity reduction techniques to be specified is a restriction of the maximum transport block size (TBS) to 1000 bits. This restriction is significantly lower than the maximum TBS that can be handled by existing UE categories in LTE. The lower maximum TBS requires less processing and buffering in the UE and allows for a less complex and less costly UE design.
The Third Generation Partnership Project (3GPP) specification TS 36.302, “Services provided by the physical layer”, V11.4.0 (2013-09) describes services provided by the physical layer in LTE. An LTE UE is required to be able to receive simultaneous transmissions on parallel physical channels according to the downlink reception types specified in TS 36.302, V11.4.0, Table 8.2-1 and the downlink reception type combinations specified in TS 36.302, V11.4.0, Table 8.2-2. For example, according to the tables, an LTE UE in Radio Resource Control (RRC) idle mode needs to be able to receive the broadcast channel (BCH), paging channel (PCH) and system information transmitted on the downlink shared channel (DL-SCH) in parallel. The DL-SCH is scheduled with a System Information (SI) Radio Network Temporary Identifier (SI-RNTI). An LTE UE in RRC connected mode needs to be able to receive the BCH, system information transmitted on the DL-SCH, and user data transmitted on DL-SCH. The DL-SCH is scheduled, for example, with a Cell-RNTI (C-RNTI).
If the same requirements were applied to a low complexity UE supporting a maximum TBS of 1000 bits, then either the total required buffering needs would become significantly larger than what would be required to support 1000 bits of user data, or the 1000 bits have to be shared between user data and other transmissions, which would mean a significant reduction of user data rate. For example, system information transmitted on DL-SCH with downlink control information (DCI) format 1A can amount to 2216 bits.